1. Field of the Invention
The present invention relates to a gas discharge tube; and, in particular, to a gas discharge tube for use as a light source for a spectroscope, chromatography, or the like.
2. Related Background Art
As techniques in such a field, those disclosed in Japanese Patent Application Laid-Open Nos. HEI 7-326324 and HEI 8-222185 have conventionally been known. In the deuterium lamps described in these publications, a sealed envelope is constituted by a side tube made of glass and a stem made of glass, stem pins are secured to the stem, anode and cathode sections are secured to the respective stempins, and the sealed envelope is filled with about several Torr of deuterium gas. Such a deuterium lamp is utilized as a stable UV light source.
Since the conventional deuterium lamps are configured as mentioned above, however, there have been problems as follows.
Namely, since the above-mentioned sealed envelope is made of glass as a whole from the viewpoint of freedom in processing, the temperature at the junction between the side tube made of glass and the stem made of glass exceeds 1000xc2x0 C. when they are thermally fused to each other. As its countermeasures, it is necessary to employ a floating structure in which the anode and cathode sections are separated from the junction, whereby the sealed envelope increases its dimensions, which inevitably enlarges the deuterium lamp itself.
In order to overcome the problems mentioned above, it is an object of the present invention to provide a gas discharge tube which attains smaller dimensions and easier assembling at the same time.
In the process of carrying out experiments for making the gas discharge tube smaller, the inventors have prepared prototypes which are made of a metal all but the light projection window of the side tube. As a result, it has been found that only about several tens of degrees of heat apply to the anode and cathode sections at the time of joining the side tube and the stem to each other, so that there are no thermal damages to the anode and cathode sections even in a structure in which the side tube is made so small that the cathode and anode sections are disposed closer to the side tube. The present invention is achieved according to this finding.
Namely, in order to overcome the above-mentioned problems, the gas discharge tube of the present invention is a gas discharge tube having a sealed envelope at least a part of which transmits light. The sealed envelope is filled with a gas and is provided with anode and cathode sections disposed therein. The electric discharge is generated between the anode and cathode sections, so that the light-transmitting part of the sealed envelope emits predetermined light outside. The gas discharge tube comprising a focusing electrode plate disposed between the anode and cathode sections and provided with an opening for focusing an electron directed from the cathode section to the anode section. The cathode section is disposed so as to be spaced from a line connecting the anode section and the opening of the focusing electrode plate to each other. The sealed envelope comprises a stem for securing the anode and cathode sections within the sealed envelope by way of respective stem pins independent from each other, at least respective securing portions of the stem pins being an insulator, an outer peripheral part of the stem being made of a metal, a side tube, made of metal, surrounding the anode and cathode sections and being joined to the outer peripheral part of the stem by welding, and a light projection window made of glass and secured to the side tube on the line connecting the anode section and the opening of the focusing electrode plate to each other.
According to the present invention, the side tube is made of a metal, at least the outer periphery of the stem is made of a metal, and they are joined to each other by welding. As a consequence, the discharge tube itself attains smaller dimensions while the assembling thereof is made easier by welding. Also, since the side tube has small dimensions and is made of a metal, its handling property improves extremely. Since the side tube is formed from a metal, the gas discharge tube is encouraged to have a wider range of processed forms, and is prospective for mass production.
The stem may be constructed by attaching a metal-made junction to the periphery of a glass-made body, or constructed by a metal-made body while a glass-made insulating portion is provided between the body and the stem pins.
Preferably, each of joint portions of the outer peripheral part of the stem and the side tube has a flange portion being secured to each other by welding. Such a configuration remarkably improves the easiness in assembling the side tube and the stem to each other. Also, such a flange portion can be provided with a positioning portion for arranging the gas discharge tube, so as to be utilized as a reference position with respect to the light-emitting part of the gas discharge tube.
Preferably, a wall face of the side tube is coated with a glass material or ceramic material. When the side tube is made of a metal, then some gases filling the sealed envelope may be transmitted through or occluded in the side tube. In this case, the gas pressure within the sealed envelope decreases with time, thereby yielding a fear of shortening the life as a gas discharge lamp. If the wall face of the side tube is coated with a glass material or ceramic material, then the reaction and occlusion between the side tube and gases can be prevented from occurring, whereby the degree of freedom in selecting the material and thickness of the side tube increases.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.